-LRB- CNN -RRB- -- Trucks carrying supplies to NATO troops crossed from Pakistan into Afghanistan for the first time in seven months on Thursday after Islamabad agreed to reopen routes , officials said .

The four trucks , under heavy security , crossed the border from Chaman in Pakistan 's Balochistan province .

Because Afghanistan is landlocked , many supplies for NATO-led troops fighting Islamic militants have to be trucked in from Pakistan .

On Tuesday , Islamabad decided to reopen the crucial supply routes shut down on November 27 , a day after coalition forces mistakenly killed 24 Pakistani troops .

The incident plunged U.S.-Pakistan relations to an all-time low .

The Pakistani routes offer a shorter and more direct route than the one NATO has been using since November that went through Russia and other nations , avoiding Pakistan altogether .

It has cost the U.S. $ 100 million more a month to use the alternative northern routes .

Imran Khan , founder of the Pakistan Tehreek-e-Insaf -LRB- Movement for Justice -RRB- party , lambasted the decision to reopen the routes , saying it was done without meeting conditions set forth by Parliament .

He also criticized the incumbent government as being a pawn of the United States .

The talks to reopen routes had been stuck on two key issues -- Pakistan 's demand to charge more per container shipped across its border , and Pakistan 's demand that the United States apologize for the friendly fire incident in November 2011 .

Pakistani Taliban issue threats over reopening of NATO supply routes

On Tuesday , U.S. Secretary of State Hillary Clinton apologized .

`` We are sorry for the losses suffered by the Pakistani military . We are committed to working closely with Pakistan and Afghanistan to prevent this from ever happening again , '' Clinton 's statement said .

Until her apology , the U.S. government had only expressed regret over the incident , but had not issued a direct apology .

Under Tuesday 's announcements , Pakistan agreed not to impose any transit fee with the reopened routes , Clinton said in a statement .

The Pakistani route costs about $ 250 per truck . Pakistan had been seeking $ 5,000 per truck as a condition of reopening the supply lines , which the United States refused to pay .

The U.S. military will now pay Pakistan $ 1.1 billion it owes as part of the deal struck to reopen the NATO supply lines , according to U.S. officials who had knowledge of the agreement 's details but were n't authorized to speak publicly .

The money is part of a U.S. military program called `` coalition support funds , '' which reimburses the Pakistani military for counterterrorism efforts . The U.S. halted paying the bills from Pakistan as tension rose between the two countries .

The Pentagon will consult with Congress about paying the bills prior to paying Pakistan in full , according to one of the U.S. officials .

Meanwhile , the Pakistani Taliban has threatened to attack NATO trucks , saying the supplies are used to target its members fighting against occupation in Afghanistan .

Transporters who resume supplies will be `` considered a friend of the U.S. '' and will face the consequences , a spokesman for the militant group said Wednesday .

Taliban have attacked NATO supplies in the past , and killed drivers and other crew .

U.S. and NATO secure exit route from Afghanistan

Journalist Ayza Omar contributed to this report .

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NEW : Party leader Imran Khan criticizes decision to reopen routes

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Because Afghanistan is landlocked , supplies have to be trucked in from Pakistan

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Pakistan reopens routes after Clinton apologizes for `` friendly fire '' incident that killed 24

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Transporters who resume supplies will face consequences , the Taliban say